使用Win.Forms控件在C＃中进行多线程处理

Question

I'm beginner in C#. And i have problem with threads when i using win.forms. My application freezes. What the problem with this code? I'm using microsoft example from msdn . Here's my code:

    delegate void SetTextCallback(object text);

    private void WriteString(object text)
    {
        // InvokeRequired required compares the thread ID of the 
        // calling thread to the thread ID of the creating thread. 
        // If these threads are different, it returns true. 
        if (this.textBox1.InvokeRequired)
        {
            SetTextCallback d = new SetTextCallback(WriteString);
            this.Invoke(d, new object[] { text });
        }
        else
        {
            for (int i = 0; i <= 1000; i++)
            {
                this.textBox1.Text = text.ToString();
            }
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {

        Thread th_1 = new Thread(WriteString);
        Thread th_2 = new Thread(WriteString);
        Thread th_3 = new Thread(WriteString);
        Thread th_4 = new Thread(WriteString);

        th_1.Priority = ThreadPriority.Highest; // самый высокий
        th_2.Priority = ThreadPriority.BelowNormal; // выше среднего
        th_3.Priority = ThreadPriority.Normal; // средний
        th_4.Priority = ThreadPriority.Lowest; // низкий

        th_1.Start("1");
        th_2.Start("2");
        th_3.Start("3");
        th_4.Start("4");

        th_1.Join();
        th_2.Join();
        th_3.Join();
        th_4.Join();
    }

Answer 1

There is a deadlock - UI thread is waiting for threads to complete with Thread.Join() while the worker threads are trying to send a message to UI using blocking Control.Invoke() . Replacing the Invoke in the thread code by BeginInvoke() will make the deadlock go away

 if (this.textBox1.InvokeRequired)
    {
        SetTextCallback d = new SetTextCallback(WriteString);
        // BeginInvoke posts message to UI thread asyncronously
        this.BeginInvoke(d, new object[] { text }); 
    }
    else
    {
        this.textBox1.Text = text.ToString();
    }

Answer 2

It freezes because of the Join calls. Thread.Join() makes the current thread wait after another one is complete.